Luminous electric signs of the inert gas-filled tube type have long been employed in commercial and business establishments to provide decoration and/or impart information. Typically, such signs are referred to as "neon signs" and may be hung or placed in various locations, such as storefront windows, to advertise a product, decorate, or provide message information.
The tubular lighting elements of the sign may be conformed into an array of desired letters or decorative shapes, as in a glass tube-bending operation, and the array is supportably attached by suitable brackets or wires to a rigid open frame, to a support backing, or in some form of housing or box.
In luminous signs of the neon tube type, it is desirable to protect the glass tubular lighting array from breakage, and to protect the various elements of the sign from collecting dust, foreign particles, and the like. In daylight conditions, it is often desirable that the lighted tubular array be backed by an opaque material for light containment and to provide solid background for better visibility of the sign.
It is also known to provide luminous electric display units, typically called electric blackboards, wherein a fluorescent or photoconductive plate, such as an acrylic plastic board, is edge lighted by a light-emitting element to concentrate light in the board whereby hand written information placed thereon by suitable means, such as water-soluble erasable high-pigment crayons has a glow or brightness to display the information contained on the board.
Luminous electric display units of the types described are disclosed in the following U.S. patents:
______________________________________ U.S. Pat. No. 1,654,255 U.S. Pat. No. 2,082,523 U.S. Pat. No. 2,763,948 U.S. Pat. No. 3,085,224 U.S. Pat. No. 4,903,172 ______________________________________